FIG. 1 is a map showing the layout of streets and lots for a hypothetical new residential development. The map covers an area 10 that includes streets 12 and a plurality of lots 14. The problem addressed by this invention is the selection of distribution equipment sites and routing corridors for providing utilities such as electricity, gas, etc. to the lots in area 10. The description to follow will use the provision of underground electrical supply to illustrate the principles of the invention. However, it will be apparent that the techniques described can be applied to distribution systems for other utilities.
The design of an underground electrical distribution system for a new residential development is a common task for electrical utility engineers. This type of design is presently carried out manually, using rules of thumb and experience gained from previous problem solutions. The result is that the distribution system is usually overdesigned, resulting in a waste of capacity.
Since the early days of computers, there have been attempts to computerize some of the activities in the process of distribution system design. Some progress has been achieved in automating routine tasks, such as substation wiring diagrams. Computerized methods have also been developed for well-defined engineering procedures, such as power flow and voltage drop calculations, and fault analysis. Relatively little progress has been made, however, in automating the important and difficult issues of transformer siting and the routing of secondary wiring. Transformers are used to convert the "primary" 12.5 kV electrical supply into the "secondary" 120 V supply that will be delivered to the individual lots via "secondary wiring." Typically, there will be one transformer for every 5 to 15 lots, and the transformer needs to be sited appropriately with respect to the lots that it will serve. In addition, the secondary wiring connecting each lot to its transformer needs to be routed and sized appropriately.
FIG. 2 represents an example of a solution to the design problem posed by FIG. 1. In FIG. 2, a plurality of transformers 20 have been positioned in selected lots. Collectively, the transformers serve all of the lots in area 10 except shaded lots 16 that do not have frontage on one of the streets 12 in the plat, it being assumed that such lots are outside the scope of the design problem. Each transformer converts 12.5 kV primary voltage into 120 V secondary voltage, and delivers secondary voltage to a plurality of lot supply points 22 via secondary wiring 24. In some cases, the connection is via a handhole 26 that is a distribution device for secondary voltage. The present invention provides a computer based method for the generation of a design solution, such as the one shown in FIG. 2, in light of the numerous constraints that are typically placed on such a solution.
Transformer siting and the routing of secondary wiring are ill-structed and open-ended problems that are difficult to automate or computerize with conventional approaches such as operational research or CAD. One difficulty lies in the need to process spatial data such as lot and street placement, existing utility corridors, natural obstacles, etc. A second problem is that siting and routing involves multiple, interdependent goals and constraints that make the design problem difficult to formulate. To apply conventional optimization routines from operational research theory, a well-defined objective function must be derived in an algorithmic form. However, due to the ill-structured and open-ended nature of the utility distribution problem, it is not possible to derive an objective function without sacrificing decision factors. These facts make conventional procedural optimization methods inappropriate for solving utility distribution design problems.